This invention relates to a process for the hydrophilic finishing of fibers, which exclusively or predominantly contain polyolefins or polyesters, or of nonwovens containing polyolefin or polyester fibers and to fibers or nonwovens which are given a hydrophilic finish by this process.
In the manufacture of sanitary articles, such as diapers or sanitary napkins, absorbent materials are used to absorb aqueous liquids. In order to prevent direct contact with the absorbent material during wear and to increase comfort, the absorbent material is wrapped in a thin water-permeable nonwoven. The nonwovens used for this purpose are normally made of synthetic fibers, such as polyolefin or polyester fibers, because fibers such as these are inexpensive to produce, exhibit good mechanical properties and, in the case of polyolefin, can be thermobonded. However, untreated polyolefin or polyester fibers are not suitable for this particular application because, in view of their hydrophobic surface, they are not sufficiently permeable to aqueous liquids. Accordingly, the fiber surface has to be made hydrophilic by a corresponding finish. It is also desirable that the hydrophilic finish of the fibers should remain intact for as long as possible without any reduction in the permeability to water of the nonwoven. If nonwovens of the type in question are made up, for example, into diapers, the diapers thus produced can be subjected to repeated stressing without becoming leaky. In this way, the wearing time of the diapers is increased and the waste caused by used diapers can be reduced accordingly.
U.S. Pat. No. 5,045,387 describes, for example, a formulation for the hydrophilic finishing of polyolefin fibers which contains a mixture of an alkoxylated ricinoleic acid derivative, a hydrogenated ricinoleic acid derivative, a C.sub.18 fatty acid and a polyalkoxylated polymethyl siloxane. EP 372 890 B1 discloses fibers which contain polyolefins or polyesters and which have been treated with a finish containing a fatty acid diethanolamide, a polyether-modified silicone, a sorbitan fatty acid ester and a metal salt of an alkyl sulfonate. The disadvantage of finishes such as these lies above all in their high price. In addition, correspondingly finished fibers show poorer behavior in the nonwoven production process, particularly during thermobonding, which results in reduced strength of the nonwoven. EP 395 099 A2 describes absorbent materials, more especially tampons of rayon or polyester fibers, which are finished with glycerol monolaurate as a bacteriostatic, toxin-inhibiting component. There is no mention of hydrophilic finishing of the fibers. DE 33 09 530 C1 describes sanitary absorbent towels, such as diapers or tampons, which are provided with a liquid-permeable covering film impregnated with a mixture of triglycerides and/or partial glycerides of C.sub.8-18 coconut oil fatty acid as a skin-care component. However, the time taken by diapers with a liquid-permeable covering film according to the teaching of the German patent in question to absorb an aqueous sodium chloride solution at 20.degree. C. increases by 50%.
The problem addressed by the present invention was to provide an improved process for hydrophilically finishing polyolefin- or polyester-containing fibers or nonwovens containing polyolefin or polyester fibers, the hydrophilic finish applied remaining intact, even after repeated wetting.